Differential transformer



NOV. 25., 1958 R, A, FRYKLUND 2,862,193

DIFFERENTIAL TRANSFORMER Filed March 13, 1958 2 Sheets-S hee1. 1

l I I l I :Hllllllllllll 1N VENTOR i BMEMMMM ATTORNEYS R. A. FRYKLUND DIFFERENTIAL TRANSFORMER Nov. 25, 1958 2 Sheets-Sheet 2 Filed March 15, 1958 INVENTOR R0fier$A.F1yMu/mi WaW,Wa/a% ATTORNEYS DIFFERENTIAL TRANSFORMER Robert A. Fryklund, Dedham, Mass., assignor, by mesne assignments, to Dresser Industries, Inc., Dallas, Tex., a corporation of Delaware Application March 13, 1958, Serial No. 721,156

Claims. (Cl. 336119) This invention relates to transformer structure, and more particularly to the physical make-up and arrangement of components of a differential transformer.

Differential transformers have been used for a large number of purposes in the control field, as well as in the instruments field. They are employed to translate mechanical movement into an electrical voltage and generally include a primary and a pair of secondary windings, with the secondaries connected in opposition. so as to furnish zero voltage output when the movable member of the transformer is in its neutral position. When that movable member is moved from its neutral position, the voltage in one of the secondaries becomes larger than that in the other so that a net voltage is obtained, the phase of that voltage indicating the direction in which the movable member was displaced. More specifically, the apparatus of the present invention relates to a differential transformer in which the primary winding is movable between and with respect to a pair of spaced secondary windings. The present invention constitutes an improvement over structure described in my Patent No. 2,470,244, issued May 17, 1949. That patent discloses a differential transformer employing a rather peculiar arrangement of cores and windings so as to permit relative movement between the primary winding and the secondary windings. In contrast, the structure of the present invention is designed in such fashion that it can employ standard transformer laminations and conventional form-wound or bobbin-wound coils, so that the manufacturing cost of the differential transformer of this invention is substantially less than that of my prior patent.

The apparatus of the present invention constitutes a very compact assembly, which nevertheless has each part readily accessible for replacement or repair, yet the output of the transformer is especially large.

The apparatus of-the invention, generally speaking, includes a pair of U-shaped cores arranged in S configuration, with the primary winding surrounding the abutting legs, and a third and a fourth U-shaped core having their open ends facing the open ends of the primary cores,

the secondary coils embracing the third and fourth cores.

The secondary cores are fixed to the base of the apparatus, while the primary cores are supported by a carrier which is spring-supported from the base and which is movable to vary the dimensions of the gaps between the primary and secondary cores.

The invention will now be described more fully in conjunction with drawings showing a preferred embodiment thereof.

In the drawings,

Fig. 1 is a plan view of a preferred embodiment of the invention;

Fig.2 is an elevational view of the apparatus of Fig. 1;

Fig. 3 is an end view of the apparatus of Figs. 1 and 2;

Fig. 4 is a sectional view taken along line 4-4 of Fig. 1; and,

Fig. 5 is an exploded view showing the relationship of the cores, the base, and the carrier of the apparatus.

States Patent 0 2,862,193 Patented Nov. 25, 1958 Referring to the drawings, the apparatus to be described is supported on a base 1 which carries a pair of pedestals 2 and 3 at opposite ends thereof. U-shaped stacks of laminations of ferromagnetic material 4 and S are bolted to the pedestals 2 and 3, respectively, and their inner legs carry bobbinor form-Wound secondary coils 6 and 7.

The apparatus also includes a pair of leaf springs 8 and 9 each having one of their ends bolted to the pedestals 2 and 3, respectively, and their other ends bolted to a carrier 10, which is supported above the base. The leaf springs permit the carrier to be reciprocated lengthwise of the base 2, and the spacing between the base and the carrier permits relatively frictionless movement between these two members.

The center portion of the carrier 10 carries a pair of stacks of U-shaped laminations 11 and 12 which are bolted to the carrier. The stacks 11 and 12 form cores for the primary of the transformer and have their inner side legs abutting and their open ends facing in opposite directions. The primary coil 13 is a bobbinor formwound coil like the two secondary coils, and embraces the two inner legs of cores 11 and 12. The legs of core 12 are substantially colinear with the legs of secondary core 4, while the legs of core 11 are substantially colinear with the legs of secondary core 5. All of the cores 4, 5, 11, and 12 are of identical configuration and equal size.

As is evident from the drawings, the cores 11 and 12 are bolted to the carrier 10 so that movement of the carrier in a direction perpendicular to the planes of leaf springs 8 and 9 will move the cores 11 and 12 either toward core 4 or toward core 5. Cores 4 and 5 are spaced apart in the direction of movement of the carrier a distance greater than the dimensions of cores 11 and 12 in the same direction. The gap size may be of the order of $0.005". The increase or decrease in the sizes of the gaps between cores 11 and 12 and the opposing secondary cores 4 and 5 caused by movement of the carrier will change the relative magnitudes of the voltages induced in the secondary windings.

In order to permit movement of the primary coil and its cores with respect to the secondary coil and cores, the carrier is provided with an actuator member 14 which is bolted to the carrier.

The operation of the apparatus described above will be apparent from the description. When the actuator 14 is moved toward the left of Fig. 1 of the drawings, the spacing between the primary cores and the secondary core 4 will be decreased and the voltage across that secondary coil will increase. At the same time, the gap between the primary cores and secondary core 5 will increase and the voltage across coil 7 will decrease. With the coils 6 and 7 connected in series opposition, and with the voltage across coil 6 predominating, there will be an output voltage from the transformer equal to the difference between the two core voltages and of the phase of coil 6. In contrast, when the actuator 14 is moved in the opposite direction, the voltage across coil 7 will predominate and the phase of the output voltage will be opposite to that obtained when the actuator is moved in the first-mentioned direction.

It will be apparent that the apparatus described is relatively simple and compact, and it is extremely easy to assemble. Further, the coils, being bobbinor formwound, can readily be replaced if that becomes necessary 3 I claim: 1. A differential transformer comprising a primary coil, a pair of secondary coils, a pair of U-shaped magnetic cores arranged with a side leg, of one core adjacent a side leg of the other core and with their openend's oppo site so as to form substantially a. letter S, said primarycoil embracing the adjacent legs of said pair of cores;

a third and a fourth U-shaped magnetic-core respectively.

arranged with their open endsfacing; the open. ends of one and the other of said pair of cores and with legs substantially colinear with the legs thereof, said secondary coils embracing said thirdand fourth cores, respectively, a base, said third and fourth cores being, fixed to the base, and means mounting said pair of cores with respect to said base for movement toward and away from said third and fourth cores.

2. The apparatus of claim 1' in which each of said cores is formed by stacks of U-shaped laminations.

3. The apparatus of claim 1 in which said mounting means comprises a pair of leaf springs each having one end fixedly connected to the base and having its other end fixedly connected to said pair of cores.

4. A differential transformer including a base, a carrier, a pair of parallel leaf springs each having one of its ends fixedly connected to opposite ends of the base and its other end fixedly connected to said carrier, said carrier being spaced from said base, a pair of stacks of U-shaped ferromagnetic laminations each forming a core and fixedly mounted in coplanar fashion on said carrier With adjacent legs abutting and open ends oppositely facing, a primary coil embracing the adjacent legs of said pair of cores, a third and a fourth stack of U-shaped ferromagnetic laminations each forming a core and fixedly mounted at opposite ends of said base with open ends respectively facing one and the other of said pair of cores and with legs colinear therewith, a pair of secondary coils respectively embracing said third. and fourth cores, said third and fourth cores being spaced in the direction of movability of the carrier a distance greater than the dimension of said pair of cores in the same direction, and an actuator fixedly connected to said carrier and operable when moved" in a direction perpendicular to the planes of said leaf springs to move said pair of cores respectively toward and away from said third and fourth cores to vary the coupling between primary and secondary coils.

5. The apparatus of claim 4 in which said secondary coils each embrace the inner leg of its core.

References Cited in the file of this patent UNITED STATES PATENTS 2,470,244 Fryklund May 17, 1949 

